Thanks so much! I particularly liked the division to break the rock and had other ideas for similar mechanics but didn't have time to implement them. I liked the idea of not only teaching maths as sums like in school, but also giving a physical representation of what that actually means, since some people learn better like that and get bewildered by just numbers.
I was a little concerned that the 'backwards' sums might be confusing - e.g. you need to first add a division operator to a number, then use that number on another number, so instead of the usual order of sums in maths (4 / 2 =) you kind of do it backwards (2 -> /2 -> 4 = ) but that's the only way I could implement the use of operators on the environment (e.g. rock / 4).
I'm especially happy your 8-year-old liked it! That's the target audience after all! :)
Thanks again!